Solubilisation of mucilage induces changes in Microcystis colonial morphology

Abstract

This study was conducted to determine if the seasonal succession of Microcystis based on classification using its morphological characteristics was a result of changes in the colonial morphology of the same Microcystis species. The seasonal variation of Microcystis colonial morphology in Lake Taihu was investigated from June 2011 to November 2011 and found that M. ichthyoblabe, M. wesenbergii and M. aeruginosa successively dominated in Lake Taihu. Moreover, Microcystis colonies collected from Lake Taihu were soaked in deionised water in darkness at 4 °C, which resulted in changes in colonial morphology from a morphotype characteristic of M. ichthyoblabe to those characteristic of M. wesenbergii and M. aeruginosa. However, this change was not observed when samples were soaked in raw water from Lake Taihu. The change in morphology was also observed when samples were soaked in cationic solution containing only K, Na, Mg or Fe, but not in 20 mg L−1 Ca solution. These results suggest that the seasonal succession of Microcystis species can be considered a colonial morphological change induced by mucilage solubilisation.